Glossary - Autonomous and Autonomic Systems - page 243

three spacecraft-body unit vectors and the three reference axes relative to
which the spacecraft orientation is defined.
Attitude quaternion A specification of the spacecraft orientation in
quaternion format.
Attitude sensors Spacecraft hardware and electronics providing measure-
ment data that can be used to determine the spacecraft orientation or
changes in the spacecraft orientation.
Autonomic Of or pertaining to the capacity of a system to control its own
internal state and operational condition.
Autonomic communications A research field with the same motivators
as the autonomic computing concept with particular focus on the comm-
unications research and development community (see SAC).
Autonomic computing Overarching initiative to create self-managing
computer-based systems, with a metaphor inspired by the biological
autonomic nervous system.
Autonomic element An autonomic manager and a managed component
considered together.
Autonomic manager A control loop and components to provide auto-
nomic self-* for the managed component.
Autonomic systems Often used synonymously with autonomic comput-
ing; sometimes used as a synonym for autonomicity from a systems per-
spective, and sometimes used in the sense that AutonomicSystems =

AutonomicComputing + AutonomicCommunications .
Autonomicity The quality of having an autonomic capability.
Autonomy A system's capacity to act according to its own goals, percepts,
internal states, and knowledge, without outside intervention.
Celestial-pointer A spacecraft whose fine-pointing science instruments are
oriented toward “fixed” points on the celestial sphere. For example, a
spacecraft that slews from one attitude to another to observe a series of
X-ray point-sources would be a member of the class of celestial pointers.
Center of mass Average position of a system of objects, weighted in pro-
portion to their masses.
Charge coupled device star tracker A star tracker that detects stars by
digitally scanning an array of photosensitive components (pixels). The
star tracker integrates the electrical charge in the pixels “struck” by (for
example) starlight. The measurement is performed by reading the pixel
output line by line.
Coarse Sun sensor A device that measures photocell output as a function
of Sun angle. Since the amount of energy hitting the photocell varies as
the cosine of the Sun angle (normal incidence for null Sun angle, grazing
incidence for 90 ◦ Sun angle), CSSs are also referred to as cosine detectors.
Note that this scheme provides an analog representation of the Sun angle.
Command quaternion Desired spacecraft orientation, with respect to an
inertial reference frame, expressed in quaternion format.